The last one is often 800 m away from the other two and by the time needed to get there, those 2 are up again ...
It's best to ignore them and proceed with the mission as usual, maybe at some point they group up for a brawl. Not worth the hassle otherwise.

Keep anything you like.
Also Sibear, I'll probably never use it, but it costs too much cryotic farming to just throw it away.
All Vandals, Prisma and Wraith variants.
Most event and clan lab weapons (Embolist for life!). Except for Hema. I don't want to see that enourmous waste of mutagen samples ever again.

Vauban.
Frame concept was awesome, but the game evolved, became faster and easier and Vauban aged very badly.
Bounce was once useful to hop on the ledges or high ground, but then parkour 2.0 bullet jump made it useless.
Bastille was great cc tool, but the game required cc back then. Then constant powercreep made most forms of hard cc obsolete and now it's easier just to wipe entire tileset with 1 button.
Vortex combined with Torid was ultimate defense againt infested in long survival/defense missions, but ... yeah, well, press 4.